Inductive power transfer apparatus

ABSTRACT

A magnetic flux pad for receiving or generating magnetic flux. The pad includes two pole areas (11, 12) associated with a magnetically permeable core 14. Coils 17 define the pole areas. The pad allows useable flux to be generated at a significant height above a surface of the pad.

The present application is based on and claims the benefit of pendingU.S. patent application Ser. No. 13/138,298 filed Jul. 28, 2011 which isa 371 of International Application Number PCT/NZ2010/000018 filed onFeb. 5, 2010, which claims priority from New Zealand Application 574677filed Feb. 5, 2009 and New Zealand Application 576137 filed Apr. 8, 2009and the entire contents of each of which are herein incorporated byreference.

FIELD OF THE INVENTION

This invention relates to apparatus for generating or receiving magneticflux. The invention has particular, but not sole, application to a lowprofile, substantially flat device, such as a pad, for power transferusing an Inductive Power Transfer (IPT) system.

BACKGROUND

IPT systems, and use of a pad including one or more windings that maycomprise the primary or secondary windings for inductive power transfer,are introduced in our published international patent application WO2008/140333, the contents of which are incorporated herein by reference.One particular application of IPT power transfer pads is electricvehicle charging. IPT power transfer pads are used both in the vehicleas a power “pick-up” device (i.e. the secondary side winding of the IPTsystem), and at a stationary location such as a garage floor as the“charging pad” (i.e. the primary side winding) from which power issourced.

In the development of pick-ups for inductively charging electricvehicles a problem of some concern is the clearance available under thevehicle. With conventional pick-up circuits power in sufficientquantities can be provided at distances up to perhaps 100 mm at whichtime the coupling factor becomes so small that it becomes impractical.

It is generally conceded that the power required to charge a typicalelectric vehicle overnight is about 2.0 kW, so that in an overnightcharging mode some 24 kWH can be transferred. With modern electricvehicles this is enough energy to travel more than 100 km and is idealfor small vehicles used for tasks such as dropping children at schools,running errands, short commutes and the like.

Inductively coupled chargers commonly use two power pads that arecircular in shape and may have dimensions of 400 mm diameter by 25 mmthick as shown in FIG. 1. However, to use an inductive charger such asthis the vehicle must be positioned relatively accurately over thecharging pad—typically within 50 mm of perfect alignment—and theseparation between the power pad on the vehicle and the power pad on theground must be closely controlled. In principle inductive power transfermay be accomplished for vertical spacings between 0 mm and 100 mm but ifthe system is set up for 100 mm it will have quite a large reduction inpower at 120 mm and will be inoperable below 50 mm. This state ofaffairs occurs because both the self inductance and the mutualinductance of the power pads vary widely as the distance between thepads changes. The self inductance and the mutual inductance as afunction of the separation for two identical circular pads that have theconstruction of FIG. 1, are shown in FIG. 2. Thus at 100 mm the powerpad receiver or pick-up may have a pick-up voltage of 100 V and a shortcircuit current of 5.0 A for a power rating of 500 W. If the IPT systemelectronics operates with a Q factor of 4, then 2 kW can be transferredto the battery though there are still difficulties to overcome inproducing the power needed at the appropriate battery voltage.

The induced voltage in the pick-up pad (i.e. the vehicle mounted powerpad) is very separation sensitive—corresponding to the variation inmutual inductance shown in FIG. 2—so that at 120 mm it is reduced byapproximately 40% while at 50 mm it is increased by a factor of 2. Areduction in power means that the vehicle does not get fully charged inthe usual time, but the more challenging situation is that at smallerseparations the power transferred may be so high that the components ofthe circuit are overloaded. Also, as the separation is reduced the selfinductance of the pick-up coil also changes so that the circuit operatesoff-frequency putting extra stress on the power supply. As theseparation gets smaller still this stress on the power supply caused bythe non-tuned pick-up on the primary side cannot be sustained and thesystem must be shut down. In practice it is feasible to operate with aseparation between 40 and 100 mm but a larger range is too difficult.

A range of separation from 40 to 100 mm is quite small. If the vehiclehas a relatively high ground clearance then either the power pad on thevehicle has to be lowered or the power pad on the ground has to beraised. Automatic systems for doing this compromise the reliability ofthe charging system. Alternatively the pad on the ground can be on afixed but a raised platform but such a pad is a tripping hazard when acar is not being charged and this situation is generally to be avoidedin a garage or other location involving vehicles and pedestrians.

The known power pad construction of FIG. 1 comprises an aluminium case 1containing typically eight ferrite bars 2 and a coil 3. Current in thecoil causes magnetic flux in the ferrite bars and this flux has fluxlines that start on the ferrite bars and propagate to the other end ofthe bar in a path containing the coil that may be thought of as asemi-elliptical shape. The flux lines 4 for a single bar are shown inFIG. 3. The flux lines leave the ferrite in an upward direction andpropagate to the other end of the bar, entering it at right angles. Noflux goes out the back of the pad as the solid aluminium backing plate 1prevents it. In the actual pad the eight bars give a flux pattern shownapproximately in cross section in FIG. 4. A simulation of the actualflux pattern is shown in FIG. 4A.

From FIG. 4A it can be seen that at the highest point the flux lines areessentially horizontal. Therefore, to get the maximum separationpossible between the primary pad and the secondary pad it would beadvantageous to detect this horizontal flux. However, the horizontalflux is still relatively close to the pad (extending from the padapproximately one quarter of the diameter of the pad) and there is nohorizontal flux at all at the very centre of the power pad. Thus at thevery point where maximum flux density would be ideal—the centre—theactual usable horizontal flux component is zero.

SUMMARY

It is an object of the invention to provide an improved apparatus ormethod for inductive power transfer, or an improved IPT power transferpad, or to at least provide a useful alternative.

Accordingly in one aspect the invention provides a magnetic flux padhaving a front face and a back face for generating or receiving magneticflux in or from a space beyond the front face, the pad comprising:

-   -   two pole areas for sending or receiving flux,    -   a magnetically permeable core,    -   two coils magnetically associated with the core,    -   whereby the flux enters the pad at one of the pole areas and        exits the pad at the other pole area.

The coils are flat coils in one embodiment, and each coil may define oneof the pole areas.

The coils may be spiral wound coils.

In one embodiment the coils are located on a side of the core nearest tothe front face of the pad, and the coils and the core together form aflux path in the pad.

The core may comprise lengths of permeable material, such as ferrite.

In one embodiment the turns of the coils are spread between the poleareas. In another embodiment the turns of the coils are concentrated atareas outside the region between the pole areas, such as the areas atthe ends of the pad. The coils may each be asymmetric, the combinationof windings of a coil being wider between the pole areas than at theperiphery of the pad.

In one embodiment the coils are located immediately adjacent to eachother in the region between the pole areas. The coils may touch eachother at the region between the pole areas.

The coils may be shaped to provide the poles areas and a flux pipebetween the pole areas. The coils may also be in substantially the sameplane.

In a further aspect the invention provides a magnetic flux pad having afront face and back face for generating a magnetic flux in a spacebeyond the front face of the pad, the pad comprising:

-   -   two pole areas for sending or receiving flux,    -   a magnetically permeable core,    -   two coils associated with the core and being provided on a side        of the core adjacent to the front face of the pad,    -   whereby the pad produces an arch shaped flux in the space such        that essentially each line flux starts on one of the pole areas,        arches to the second pole area and joins on itself through the        core with essentially no flux present at the back face of the        pad.

In a still further aspect the invention provides a magnetic flux padhaving a front face and back face for receiving a magnetic flux from aspace beyond the front face of the pad, the pad comprising:

-   -   two pole areas for sending or receiving flux,    -   a magnetically permeable core,    -   two coils associated with the core and being provided on a side        of the core adjacent to the front face of the pad and adapted to        receive a horizontal flux component,    -   and a further coil magnetically associated with the core and        adapted to receive a vertical flux component.

In yet a further aspect the invention provides an IPT system including amagnetic flux pad according to any one of the preceding statements. Thesystem may also include a transmitter pad and a receiver pad accordingto the preceding statements.

The IPT system may supply power to an electric vehicle.

In a further aspect the invention provides an IPT power transfermagnetic flux transmitter or receiver including:

a magnetic flux carrying member having a relatively high magneticpermeability and having two ends, two windings electromagneticallyassociated with the flux carrying member, and the flux carrying memberhaving two flux transmission or reception regions, one region beingprovided adjacent to each end, whereby magnetic flux exists or entersthe flux carrying member substantially only at or adjacent to thetransmission or reception regions.

Further aspects of the invention will become apparent from the followingdescription.

DRAWING DESCRIPTION

One or more embodiments are described below by way of example withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of part of a known form of IPT powertransfer pad;

FIG. 2 is a graph of inductance measurements and flux linkage efficiencywith respect to height displacement for a pad such as that of FIG. 1;

FIG. 3 is a diagrammatic elevation in cross section of a part of the padof FIG. 1 showing flux lines;

FIG. 4 is a plan view and elevation of a cross section of the pad ofFIG. 1 showing flux lines;

FIG. 4A is an elevation in cross section of a computer generatedsimulation of the magnetic field (indicated by flux lines) of the pad ofFIG. 1;

FIG. 5A is a plan view of an embodiment of inductive power transferapparatus which may be provided in the form of a pad;

FIG. 5B is a side elevation of the apparatus of FIG. 19A;

FIG. 5C is a view of FIG. 5B but also showing flux lines;

FIG. 5D is a computer simulation of s cross section through a padaccording to FIGS. 5A-5C illustrating the flux lines generated by such apad in use;

FIG. 6 is a diagrammatic illustration of an electrical wiring diagramfor a further embodiment of inductive power transfer apparatus includinga centre, or quadrature coil;

FIG. 7A is an isometric view from below of a flux transmitter and fluxreceiver (oriented above the flux transmitter).

FIG. 7B is an isometric view from above of the arrangement of FIG. 7A;

FIG. 8A shows flux lines based on a simulation of the arrangement ofFIGS. 7A and 7B when the transmitter and receiver are aligned with a 200mm separation between the transmitter and receiver;

FIG. 8B shows flux lines based on a simulation of the arrangement ofFIGS. 7A and 7B when the transmitter and receiver are misaligned in theX axis direction;

FIG. 9 is a diagram of power against displacement in the X axisdirection for the arrangement of FIGS. 7A and 7B;

FIG. 10 is a diagram of power against displacement in the Y axisdirection for the arrangement of FIGS. 7A and 7B;

FIG. 11 is an illustrative diagram of a winding arrangement for coils ofa pad of the preceding figures;

FIG. 12 is a plan view of a former or support plate for construction ofa pad according to the preceding figures;

FIG. 13 is an isometric view of the former of FIG. 12, and;

FIG. 14 is an isometric view of a backing plate adapted for attachmentto the rear of the former shown in FIGS. 12 and 13.

DESCRIPTION OF EMBODIMENTS

A new concept in IPT power transfer arrangements is now disclosed. Theembodiments described in this document relate to flux transmission andreception apparatus. These are commonly (although not necessarily)provided in the form of a discrete unit which may conveniently bereferred to as power transfer pads i.e. arrangements that may beportable and which typically have a greater extent in two dimensionsrelative to a third dimension so that they may be used in applicationssuch as electric vehicle charging where one pad is provided on a groundsurface (such as a garage floor) and another in the vehicle. However,the disclosed subject matter may also be provided in other arrangementsincluding permanent structures such as a roadway for example, and doesnot need to take the form of a pad. Like reference numerals refer tolike features throughout the description.

Referring to the arrangement of FIG. 5A, a pad is shown which uses anovel “flux pipe”, generally referenced 10, to connect two separatedflux transmitter/receiver regions comprising pole areas 11 and 12. Theflux pipe provides a generally elongate region of high fluxconcentration from which ideally no flux escapes. The flux pipe 10 inthis embodiment has a core 14 which includes a magnetically permeablematerial such as ferrite to attract flux to stay in the core. Withelectric circuits there is a large difference between the conductivityof conductors—typically 5.6×10⁷ for copper; and air—in the order of10⁻¹⁴—but this situation does not pertain with magnetic fields where thedifference in permeability between ferrite and air is only the order of10,000:1 or less. Thus in magnetic circuits leakage flux in air isalways present and this has to be controlled to get the best outcome.

Flat coils or windings 17 sit on top of the core 14 to provide the fluxpipe. There is no straight path through the flux pipe that passesthrough the coils 17. Instead, the arrangement of the coils 17 meansthat flux entering the pad through one of the areas 11 or 12 propagatesthrough the relevant coil 17 into the core 14 from where it propagatesalong the core, then exits the pad out through the other area 12 or 11,and completes its path through air back to the first area 11 or 12 toform a complete curved flux path. The flux path so formed is essentiallycompletely above a front surface of the pad and extends into a spacebeyond the front surface. The arrangement of coils 17 also means thatthere is essentially no flux extending beyond a rear face of the pad.Thus, the orientation of the windings 17 ensures that the flux path isdirected in a curve out into a space in front of the front surface ofthe pad, and the spread or distributed nature of the coils 17 across theupper surface of the core 14 ensures that the flux in the centre of thepad is primarily constrained within the core. The coils 17 also definethe spaced apart pole areas so that the flux is guided into and out ofthe pad via the pole areas and forms an arch shaped loop in the spacebeyond the front surface of the pad to provide a significant horizontalflux component at a significant distance above the front surface of thepad.

In a preferred embodiment there are two coils 17 in close proximity toeach other. The coils 17 are spiral wound. In the diagrammaticembodiment illustrated in FIGS. 5A to 5C the coils 17 take the form ofArchimedean spirals, and are touching along the centre line 17A. Theflux pipe 10, comprising core 14, extends to the ends of the coils 17.The coils 17 are substantially planar and are arranged in substantiallythe same plane on one side of the core 14. The actual length of the core14 is not critical—in one embodiment it should include the centre lineof the coils 17 and should extend past the hole in the centre of eachcoil to at least the position indicated by A. The core 14 may extendunder the coil 17 to position B or even further. The holes in the coils17 define the pole areas 11 and 12 which function as fluxreceiver/transmitter regions for the pad.

In one embodiment the core 14 is made of ferrite bars in strips orlengths (not shown in FIGS. 5A-C, but illustrated in FIGS. 7A and 7B).Air-gaps are acceptable between the strips, which simplifiesmanufacture. The ideal flux paths 20 are shown in FIG. 5C and are onlyon one side of the core 14 which is an ideal situation. In principlethere is ideally no flux extending out the rear face of the pad (i.e. onthe side of the core 14 opposite to the side on which coils 17 aremounted) and therefore no aluminium screen or other flux repellingmember is required. However, in practice a light screen may be used insome embodiments as errors and imperfections in the ferrite barscomprising the core 14 can cause small leakage fluxes that should becontained.

FIG. 5D shows the result of a simulation of the pad construction inFIGS. 5A-5C when used to generate a magnetic field. As can be seen, theflux path follows a generally arch shape through the space beyond thefront surface of the pad.

Inductive power transfer pads according to the arrangement describedimmediately above are very easy to use as the leakage flux from them isvery small. They can be placed quite close to metallic objects withoutloss in performance, and they are largely unaffected by connecting wiresetc.

Second Embodiment

In a further embodiment it may be noted that the arrangement of thecoils in a receiver or pick-up pad mounted horizontally on a vehicle,for example, makes the pick-up pad sensitive to a first direction of theflux which is longitudinally directed (i.e. having a direction parallelto the core 14, and being in the X-axis direction with reference to thedrawings) with respect to the flux generator (the horizontally orientedtransmitter pad). To improve the magnetic coupling of the receiver withrespect to misalignment, a “second” coil can be arranged that issensitive to a second component of the flux that is preferably verticalwith respect to the stationary transmitter.

FIG. 6 shows an electrical schematic of a further embodiment of areceiver pad with a “horizontal” flux sensitive coil 22 now positionedin the centre and the outer two coils 17 connected out of phase toproduce a further coil sensitive to the vertical component.

For the receiving pad of FIGS. 5A-5C a further flat coil 22 can also beplaced above the flux pipe with one suitable arrangement shown in FIGS.7A and 7B, coil 22 being sensitive to the vertical component of thefield. As in the original pick-up structure, this additional coil existsonly on one side of the core 14 and therefore ideally maintains all ofthe flux lines on the side of the receiver directed towards thetransmitter.

As shown in FIGS. 7A and 7B, only the receiver is modified with acentre, or quadrature, coil 22. This second coil is particularlysensitive to misalignment in the X-direction (i.e. the horizontallongitudinal direction), but not in the Y-direction (being thehorizontal transverse direction perpendicular to the core 14). Thiscomplements the original receiver which is sensitive to misalignment inthe Y-direction, but which because of its structure is less sensitive tomovement in the X-direction. The combined output of both receiver coilsenhances the sensitivity of the receiver enabling the receiver to bepositioned nominally in the ideal position and still couple the requiredpower. FIGS. 7A and 7B also show an arrangement of spaced ferrite rodsor bars 24 that comprise core 24.

As an example, the flux lines using the pad design as shown in FIGS. 7Aand 7B without any form of compensation are shown in FIGS. 8B and 8Awith and without some misalignment. Here the transmitter pad andreceiver pad are identical except for the addition of the second“vertical flux” coil (i.e. coil 22 of FIGS. 7A and 7B) in the receiverpad. The transmitter and receiver pads both have length 588 mm and width406 mm and are separated vertically by 200 mm. The current in the coilsof the transmitting pad is 23 amps at 20 kHz. Notably the majority ofthe flux exists between the transmitter pad and receiver pad while avery small leakage flux is shown to exist outside this area. In FIG. 8Athese flux lines couple the first receiver coil, while in FIG. 8B themajority of the flux lines couple the second receiving coil (i.e. coil22 of FIGS. 7A and 7B) thereby enhancing the output power capability ofthe pick-up.

In FIGS. 9 and 10 the VA generated from the output of the receiver padcoils with and without misalignment is also shown. In FIG. 9 the totaland separate VA contribution of receiver coils from a magneticsimulation of the pads shown in FIGS. 7A and 7B is shown when thereceiver pad is misaligned (relative to its ideal position centred abovethe transmitter pad) in the X direction. In FIG. 9 curve 26 representsthe VA contribution of coil 22, curve 28 represents the combined VAcontribution of coils 17, and the remaining curve represents the totalfrom coils 17 and 22. As noted the second coil 22 substantially enhancesthe output so that if a 2 KW output were required at 0 X-offset therequired electronic tuning must boost the VA output by around 3.2. At140 mm X-offset the required electronic boost (Q) without coil 22 ismore than 17 times (which is practically difficult due to thesensitivity of the tuning required) whereas with coil 22 an effectiveboost of around 4.8 is required and that is easily achieved.

Coil 22 is not expected to be sensitive in the Y direction when thereceiver is positioned with 0 offset in the X direction. This isverified in the magnetic simulations shown in FIG. 10 where there isshown to be no contribution to the total power from the coil 22. This ishowever not required as the combined output of coils 17 is naturallysensitive in this direction. At 140 mm offset in the Y direction, a 2 KWoutput is possible with an electronic tuning (Q) of around 5.5.

Third Embodiment

Turning now to FIG. 11, a winding arrangement for coils 17 is showndiagrammatically. In this embodiment the individual turns in the coils17 are spread at that end of each winding nearer the centre of the padrelative to the ends of the pad. Thus the coils 17 are each asymmetric,the combination of windings of a coil being wider between the pole areasthan at a periphery of the pad. This embodiment allows greaterseparation of the pole areas 11 and 12 (and thus greater flux extensionbeyond the front face of the pad). The spacing between the pole areas 11and 12 may be made larger by using an oval or rectangular cross sectionlitz wire wound on the narrow edge for the pole areas and wound on theflat edge for the central flux pipe region between the pole areas.

Alternatively if the coils are wound with a round wire the spacingbetween the pole areas 11 and 12 may be made larger using gaps betweenthe windings of the flux pipe section between the pole areas. However,we have found that gaps in the individual windings over the flux pipesection are to be treated with care as they can leave holes that fluxcan leak through spoiling the efficiency of the flux pipe. We have foundthat it is preferable to keep the windings evenly spaced and if thereare gaps they should be typically less than one half to one wirediameter to keep flux losses to a minimum. In practice we have foundthat the convenience of the simple round wire makes this the technologyof choice.

In yet another embodiment, the shape of the windings 17 may assist inobtaining greater pole area separation. For example, the coils 17 may bewound in an approximately triangular shape with the apex of eachtriangle facing the centre of the pad.

Referring now to FIG. 12, a former or support plate 30 for providing apad including the winding layout of FIG. 11 is shown in plan view. Theformer 30 may be constructed from any non permeable material, such as aplastic for example. The former 30 includes a first general region 32for forming and supporting one of coils 17 (not shown) and a secondregion 38 for forming and supporting the other of the coils 17.Depressions 34 are provided for locating and supporting ferrite bars orother permeable members. Grooves 36 receive the individual wires thatcomprise the turns of coils 17 and ensure that the turns are correctlyspaced. For clarity, an isometric representation of the former 30 isshown in FIG. 13.

FIG. 14 shows a backing plate 40 adapted for location on a rear surfaceof the former 30 i.e. for location on a side of the former that isopposite the side on which the coils 17 are located, and adjacent to arear surface of the pad. Backing plate 40 may be constructed from a fluxrepelling material, for example aluminium. It is not necessary forprevention of flux exiting the rear face of a pad in use, since thedesign of the flat coils 17 and their location on the core 14substantially directs the flux into a space in front of the frontsurface of the pad. However, plate 40 can provide additional structuralsupport for the pad. Plate 40 can also act to prevent any changes in themagnetic properties of the pad (for example a change in inductance)should the pad be mounted in use adjacent to a magnetically permeablematerial for example.

The dimensions of the former 30 are approximately 790 mm by 600 mm by 25mm, and a pad constructed from such a former will have very similardimensions.

Further Practical Considerations

In practice it is prudent to ensure that the voltage at the terminals ofthe pad does not reach unsafe levels. Therefore in some embodiments,capacitance may be added in series with the windings inside the pad tolower the inductance seen at the pad terminals and therefore control thevoltage at these terminals to be within suitable limits (say 300-400V).Without this the terminal voltage could be several KV which isundesirable and potentially unsafe. Capacitance can be placed in serieswith the windings at nearly any convenient place with the apparatus.Thus in some embodiments one or more capacitors can be placed in serieswith the windings at the terminal points inside the pad housing, and inother embodiments capacitors can be distributed along the windings bybreaking the winding into suitable sections with series capacitances incase the internal voltages on a single coil are ever too high.

Therefore, the invention provides a low profile device, referred toherein as a pad, which can be used as a magnetic flux generator that canbe used to generate useful flux a significant distance from the device.The device can also be used as a receiver of flux to thereby produceelectric energy from the received field. The ability of the pad togenerate or receive flux over a significant distance is particularlyuseful for charging or energising an electric vehicle.

The entire disclosures of all applications, patents and publicationscited above and below, if any, are herein incorporated by reference.

Reference to any prior art in this specification is not, and should notbe taken as, an acknowledgement or any form of suggestion that thatprior art forms part of the common general knowledge in the field ofendeavour in any country in the world.

Wherein the foregoing description reference has been made to integers orcomponents having known equivalents thereof, those integers are hereinincorporated as if individually set forth.

It should be noted that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications may be madewithout departing from the spirit and scope of the invention and withoutdiminishing its attendant advantages. It is therefore intended that suchchanges and modifications be included within the present invention.

The invention claimed is:
 1. A magnetic flux pad having a front face anda back face, the flux pad for generating or receiving magnetic flux inor from a space beyond the front face, the pad comprising: amagnetically permeable core having a side nearest to the front face ofthe pad; and two substantially flat and substantially co-planar coils onthe side of the core, magnetically associated with the core and eachcoil defining a corresponding pole area for sending or receiving flux,wherein the flux enters the pad at one of the pole areas, exits the padat the other pole area and forms an arch between the pole areas in thespace beyond the front face of the pad, and wherein the pad has acentreline that separates the pole areas defined by the twosubstantially flat substantially planar coils, and the core does notextend past a periphery of the two substantially flat substantiallyplanar coils in a direction parallel to the centreline of the pad. 2.The magnetic flux pad as claimed in claim 1 wherein the core comprisesat least two lengths of permeable material, each of the at least twolengths of permeable material provides a flux pipe between the poleareas defined by the two substantially flat substantially planar coils,and the at least two lengths of permeable material are not in physicalcontact or immediately adjacent one another.
 3. The magnetic flux pad asclaimed in claim 1 wherein the coils are each asymmetric.
 4. Themagnetic flux pad as claimed in claim 3 wherein windings of the coilsare wider between the pole areas than at a periphery of the pad.
 5. Themagnetic flux pad as claimed in claim 1 wherein the coils are locatedimmediately adjacent to each other in a region between the pole areas.6. The magnetic flux pad as claimed in claim 1 further comprising aconductive backing plate at the back face of the pad, wherein thebacking plate is fabricated from a flux repelling material.
 7. Themagnetic flux pad as claimed in claim 1 further comprising a former ofnon-permeable material which includes a first region for forming andsupporting one of the coils, a second region for forming and supportingthe other of the coils and depressions for locating and supporting themagnetically permeable core.
 8. The magnetic flux pad as claimed inclaim 1 wherein the pad is configured to guide substantially all of theflux that exits the pad along a path that is completely above the frontface of the pad.
 9. The magnetic flux pad as claimed in claim 1 whereinthe two substantially flat substantially planar coils sit on top of theside of the core nearest to the front face of the pad, and the coreprovides a flux pipe that connects the pole areas defined by the twosubstantially flat substantially planar coils, and the two substantiallyflat substantially planar coils sit on the magnetically permeable corewith no path through the core that passes through the coils.
 10. The padof claim 1, wherein the pad is configured to project flux in an archshaped path in the space beyond the front face of the pad.
 11. Amagnetic flux pad comprising a magnetically permeable core, and twowound coils arranged substantially co-planar on the magneticallypermeable core, wherein each of the two coils defines a pole area, andthe windings of the two coils are wider between the pole areas than at aperiphery of the pad.
 12. The pad of claim 11, wherein the windings ofthe two coils between the pole areas are separated by air gaps, and theair gaps are less than a width of a conductor that the coil is woundfrom.
 13. The magnetic flux pad of claim 12 wherein the pad isconfigured to guide flux from a first pole area, defined by a first oneof the two wound coils, in a complete curved path through a space beyonda front face of the pad, to a second pole area, defined by a second oneof the two wound coils.
 14. The pad of claim 11, wherein the two woundcoils comprise a single conductor.
 15. The pad of claim 11, wherein thetwo wound coils sit on a front face of the magnetically permeable core,and the magnetic flux pad comprises a flux repelling backing plateattached to a surface of the magnetic flux pad opposite the front faceof the magnetically permeable core.
 16. The pad of claim 15, wherein themagnetically permeable core comprises at least two strips of ferrite,the at least two strips of ferrite extend between the pole areas of thetwo wound coils, and the at least two strips of ferrite are not inphysical contact or immediately adjacent one another.
 17. A magneticflux pad comprising a magnetically permeable core, and two substantiallyflat coils arranged substantially co-planar on the magneticallypermeable core, wherein each of the coils defines a pole area, themagnetically permeable core extends in a longitudinal direction betweenthe pole areas, and the magnetically permeable core is discontinuous ina direction transverse to the longitudinal direction.
 18. The pad ofclaim 17, wherein the magnetically permeable core comprises lengths ofhigh permeability material that extend in the longitudinal direction,and the discontinuities comprises gaps between the high permeabilitymaterial that are filled with a low permeability material.
 19. The padof claim 17, wherein the magnetically permeable core comprises aplurality of ferrite bars that extend substantially parallel to thelongitudinal direction of the magnetically permeable core, and theplurality of ferrite bars are separated, in the direction transverse tothe longitudinal direction, by gaps that extend substantially parallelto the longitudinal direction of the magnetically permeable core.
 20. Amagnetic flux pad having a front face and a back face, the flux pad forgenerating or receiving magnetic flux in or from a space beyond thefront face, the pad comprising: a magnetically permeable core having aside nearest to the front face of the pad; and two substantially flat,asymmetric, and substantially co-planar coils on the side of the core,magnetically associated with the core and each coil defining acorresponding pole area for sending or receiving flux, wherein the fluxenters the pad at one of the pole areas, exits the pad at the other polearea and forms an arch between the pole areas in the space beyond thefront face of the pad.